New high-speed video system uses sensors and infrared lighting to track insects across vast wilderness areas

Our ability to learn more about insect behavior, which affects ecology, health and the economy on a global scale, depends largely on appropriate recording technology. But until now, these tools have been significantly limited.

To address this problem, a research team from Albert-Ludwigs-Universität Freiburg in Germany developed an adaptable system that can be combined with different types of hardware to produce high-speed video recordings of insect flight behavior and follow, over significant distances. , their trajectories in nature.

The team describes this technology in a paper titled “High-Resolution Outdoor Insect Videography Using Fast-Lock Tracking,” published on the bioRxiv preprint server. This new work follows their previous research on this topic, published in 2020.

Existing recording methods and their limitations

Historically, insect behavior researchers have relied on direct observation to gain new insights, and more recently, they have used harmonic radar tracking to gain information about insect flight paths, particularly those of insects. bees. The resolution of this type of radar is however limited both spatially and temporally.

In laboratories, researchers have used higher-resolution cameras to study the details of insect flight behavior, but the usefulness of these cameras does not extend to insects’ natural environments, where a number of variables can play in flight function.

Researchers have also used fixed-camera videography (in which the camera can automatically track the subjects’ movements) with some success, but this method is used most effectively with a limited number of pixels for a specific width of field. Applying this method to a wider field results in lower angular resolution, while adding pixels blurs the subject’s movement. It was not possible to magnify the subject while manually and continually adjusting the camera’s aim to track movement.

Meanwhile, the combination of high-magnification optics and high-speed image tracking works with larger subjects such as birds, drones and sports balls, but low latency is needed for smaller ones. subjects like insects. Surrounding flying insects with multiple cameras or using simplified indoor backgrounds can help, but these methods also have obvious limitations.

However, retroreflectors represent a potential solution for efficient and detailed insect tracking. Informed by studies using a previously developed method for tracking insects, the research team behind this new work has dubbed the Fast Lock-On (FLO) Tracking Solution and reports on its efforts to use it to follow the flight of insects outside.

FLO monitoring with insects

To use FLO tracking with flying insects, a tiny, lightweight retroreflective marker is affixed to a subject. When the subject moves, the marker sends a signal to an optical sensor, orienting the sensor’s optical axis while minimizing the subject’s divergence from the sensor’s center point. In this study, the researchers integrated infrared illumination near the optical axis of the sensor, and oriented and tilted the optical axis to recreate the flight paths of their test subjects, including grasshoppers (Schistocerca gregaria), bumblebees (Bombus terrestris) and domestic bees. (Apis mellifera) – via the angles detected by the FLO system.

As their paper explains, “Low latency between sensor input and motor output will improve system performance and enable higher magnification optics, which ultimately can lead to additional performance gains . From a control point of view, FLO is a closed-loop design in which the displacement of the target image originating from the center of the sensor is an error angle between the angle of the insect and the angular position of the optical path under control.

The team’s test videos successfully captured the test subject’s flight “from takeoff to landing with high magnification and low motion blur,” and the insects’ appendages remained in focus during flight.

Additionally, the system is inexpensive to create and can be simply built with a computer, a low-latency digital camera, and a pan-tilt motor system. The article describes in detail the hardware, calculations for angle reconstructions and implementation methods.

Opportunities for system improvement

The team recognizes that tracking insect flights outdoors is an important problem that has not yet been fully solved. At least three major weaknesses remain. First, a momentary loss of tracking within the FLO closed-loop system could lead to complete tracking failure.

Additionally, “the system does not directly estimate the distance to the subject,” the document states. Finally, while precise calibration is not necessary for a successful tracking process, extracting and accurately determining the final 3D coordinates will require it.

Suggested improvements include using multiple FLO systems working together for improved computation via triangulation and eliminating the need for retroreflectors through the development of advanced computer vision techniques to detect objects on insects.

However, researchers remain optimistic that FLO tracking could be used to study many aspects of insect flight behavior, including several that are directly linked to broader ecological issues, such as insect responses to artificial lights. nocturnal, loss of habitats and pesticide treatments in their feeding areas.

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